1. Field of the Invention
The present invention relates in general to throttle valve control devices for controlling a throttle valve of an automotive internal combustion engine in accordance with a depressed degree of an accelerator pedal of an associated motor vehicle, and more particularly to the throttle valve control devices of a type which employs an electric actuator for actuating the throttle valve.
2. Description of the Prior Art
Hitherto, various throttle valve control devices have been proposed and put into practical use particularly in the field of wheeled motor vehicle powered by an internal combustion engine.
Some of the conventional throttle valve control devices have the following construction, which are shown in for example Japanese Patent First Provisional Publications 63-150449, 4-203219 and 6-58174.
That is, a throttle body having therethrough a throttle chamber is disposed in a part of an air intake passage of the engine. A pivot shaft extends across the throttle chamber and is rotatable about its axis. A throttle valve is secured to the pivot shaft to pivot therewith in a direction to open or close the throttle chamber. An electric motor is mounted to the throttle body to actuate the pivot shaft and thus the throttle valve. A reduction gear mechanism is arranged between the electric motor and the pivot shaft to reduce the speed of the actuating motion applied to the pivot shaft from the electric motor. A first biasing means is arranged to constantly bias the throttle valve in the direction to close the throttle chamber. A second biasing means is further arranged to bias the throttle valve against the force of the first biasing means toward an intermediate position, that is, a slightly open given position.
In addition to the above-mentioned elements, a close position adjuster is further employed, which adjusts the close position of the throttle valve. The close position adjuster comprises a projection which is integrally formed on the throttle body, and a stop screw bolt which is threaded with a threaded bore of the projection in such a manner as to adjust the length of a projected part thereof when rotated about an axis thereof. The projected part of the stop screw bolt has a head against which the throttle valve or an element rotating together with the throttle valve abuts when the throttle valve is pivoted back to the close position. Thus, by rotating the stop screw bolt about its axis, the length of the projected part thereof is adjusted and thus the close position of the throttle valve can be adjusted.
When, with the throttle valve assuming the close position, the electric motor is energized, the actuating motion of the electric motor is transmitted to the pivot shaft through the reduction gear mechanism, resulting in that the throttle valve is turned to assume a controlled open position against the force of the first biasing means. With this, the amount of air fed to the engine is controlled, and thus, the output of the engine is controlled.
When in winter the engine is stopped, the electric motor is deenergized. Upon this, the second biasing means forces the throttle valve to assume the intermediate position (viz., slightly open given position) against the force of the first biasing means. With this, undesired freeze-up of the throttle valve (viz., a phenomenon wherein the throttle valve is frozen to a barrel wall) is prevented. In fact, when, in winter, the throttle valve is kept in the close position for a long time, such undesired phenomenon tends to occur.
When, due to some reasons, the electric motor fails to be energized during operation of the engine, the second biasing means forces the throttle valve to assume the intermediate position. With this, undesired engine stop is suppressed, so that the driver can drive the vehicle but slowly to a neighboring service station for repairing the electric motor.
However, even the above-mentioned conventional throttle valve control device have failed to satisfy the users due to many reasons which are for example increase of cost, difficulty of assembly, increase in the number of parts, etc.,.